The first week of operation of the new variable speed limits on Christchurch's Northern Motorway had minimal impact on travel times during the morning peak congestion.
NZ Transport Agency Southern Regional Director Jim Harland says for a number of reasons the variable speed limits did not help reduce delays or driver frustration and he has asked motorists for their patience as work continues to find the best time to switch on the signs and help reduce traffic flows breaking down.
'This technology is new to Christchurch and we're still working to find the best time to switch on the signs each day. Last week this was not helped by daily changes in traffic volumes and an overall 12% increase in traffic volumes. We also experienced a couple of technical issues with changing the speed limits which should be resolved this week.
'We know the variable speed limits have worked well overseas and in Wellington, however to be successful it is critical drivers observe the speed limit and keep a constant speed. It is the stop/start, speed up/slow down driving that makes it near impossible to keep everyone moving.'
The variable speed limits have been introduced during morning peak-hour on the Northern Motorway to help reduce the breakdown in traffic flows when vehicles brake as they enter Belfast causing a 'slowing' ripple effect through the traffic. He says by introducing the speed limits just south of Ohoka Road where there is less traffic, the speed limits will be able to reduce the onset of flow breakdown and keep everyone moving to improve overall travel times.
'Motorists can help by observing the speed limits which are legal and enforceable, by keeping a constant speed and avoiding speeding up/slowing down, by avoiding lane changing and by limiting traffic access from the stop or give way controlled side roads when traffic is flowing on the motorway.'
Mr Harland says motorists need to think of the variable speed limits as helping to manage the number of vehicles attempting to get through a single point on the motorway at one time. "It's like pouring water through a funnel, if you pour it quickly the funnel fills up and it takes time for it to drain away. If you pour the water in slowly, it will flow through the funnel without pooling in it. That is exactly how the variable speed limits work.'
The variable speed limits are only activated when queues look like forming during heavy traffic flows.